Because David delighted in God’s Word, he knew that a just God punishes sin. David also knew that forgiveness was possible, because he knew God’s character through his Word. He knew God would be merciful to him because of his steadfast love. David knew God would blot out his transgressions according to his abundant mercy.
True delight in the Law of the Lord will produce hearts of repentance. We see this clearly in David’s response to God’s Law in Psalm 19. God’s revelation reveals to us our incompatibility as sinners with the holiness of God and the way he designed his creation to operate for his glory. Scripture explicitly teaches us that the payment for sin is death; it reproves and corrects us. As David says in Psalm 19:11, God’s Law warns us. It explicitly teaches us that “if we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness” (1 Jn 1:9). And so that is exactly what David does: he confesses his sin:
12 Who can understand his errors?
Cleanse me from secret faults.
13 Keep back your servant also from presumptuous sins;
let them not have dominion over me.
Then I shall be blameless,
and I shall be innocent of great transgression. (Ps 19:12–13)
Have Mercy on Me
Church tradition has identified seven psalms as “penitential psalms” (6, 32, 38, 51, 102, 130, 143), but several others also include themes of sorrow over sin, including 25, 39, 40, and 41.
There is perhaps a no more well-known confession of sin in all the psalms than Psalm 51. Book II of the Psalms is all about the extension of David’s rule over the nations. We remember stories of David’s exploits against the Philistines and all of the pagan nations surrounding Israel. “Saul has slain his thousands, but David his ten thousands!”